The purpose of this project is to define the morphological changes occurring in the vestibular sense organs and nerves following transtympanic labyrinthectomy. Emphasis will be placed on evaluating the magnitude and consistency of degenerative change occurring in the vestibular nerves as a function of time following labyrinthectomy. The principal question is whether vestibular nerve section has any advantage, in terms of completeness of morphological ablation, over transtympanic labyrinthectomy. The clinical significance lies in the fact that vestibular nerve section, which requires invasion of the subarachnoid space, subjects the patient to greater risk of surgical complications than transtympanic labyrinthectomy. Healthy adult cats will be subject to unilaterial transtympanic labyrinthectomy, performed as nearly identical as possible to that used on human subjects and sacrificed after postoperative survival times of one month to two years. The temporal bones will be prepared for light microscopic study by the technique of decalcification, embedding and serial sectioning after which the sensory and neural elements of the vestibular system will be quantatively evaluated. The opposite ears, prepared in osseous continuity, will serve as controls.